Solar cells using organic materials have received attention with advantages such as simple processability, diversity, inexpensive manufacturing costs and high flexibility, and have rapidly grown with the development of new materials.
Based on inexpensive costs and availability in a manufacturing process, which are the biggest advantages of organic materials, organic semiconductors are expected to appear as a core material in the manufacture of low-priced solar cells such as thin film-type devices, large area devices, flexible devices for which a roll-to-roll method may be used.
The possibility of an organic solar cell was first presented in 1970s, but the organic solar cell had no practical use since the efficiency was too low.
However, since C. W. Tang of Eastman Kodak showed the possibility of commercialization as various solar cells with a double layer structure using copper phthalocyanine (CuPc) and a perylene tetracarboxylic acid derivative in 1986, interests in organic solar cells and related researches have rapidly increased brining in a lot of progresses.
Since then, organic solar cells have made innovative progresses in terms of efficiency as the concept of a bulk heterojunction (BHJ) was introduced by Yu et al. in 1995, and fullerene derivatives of which solubility is improved such as PCBM have been developed as an n-type semiconductor material.
However, fullerene, a starting material, does not have favorable solubility thereby has low reactivity, and as a result, has a problem in that the costs of the fullerene derivatives increase due to the low yield when synthesized.
Meanwhile, the development of electron donor materials having a low bandgap and electron acceptor materials having favorable charge mobility has been continuously attempted in order to replace existing materials.